This invention relates, in general, to magnetic imaging and, in particular, to improved magnetic toner material and a process for its use. More specifically, the present invention relates to new magnetic toners containing a polymeric esterification product of a dicarboxylic acid and a diol comprising a diphenol which are useful in magnetic imaging systems employing flash fusing.
There has been introduced a magnetic imaging system which employs a latent magnetic image in a magnetizable recording surface, which image may be used in the duplicating process, for example, by toning, either once or repetitively, transferring the developed image to a suitable substrate, such as paper, and fusing the image to said substrate.
The latent magnetic image may be provided by any suitable magnetization procedure. Typically, a magnetizable layer of marking material is arranged in imagewise configuration on a magnetic substrate. Well known electrostatographic methods are sometimes used to accomplish this. The latent image may then be developed and fused. There are a number of known methods for creating the latent image which are described, for example, in U.S. Pat. Nos. 4,032,923; 4,060,811; 4,074,276; 4,030,105; 4,035,810; 4,101,904 and 4,121,261. The teachings of each of these patents is being completely incorporated herein by reference.
In once such method, the magnetizable toner is developed in imagewise configuration onto an electrophotographic recording surface. The toner is then magnetized, for example, by an electronic recording head. The layer supporting the magnetized toner is then brought into contact with a magnetizable layer and the magnetized toner magnetizes the magnetizable layer in image configuration. A latent magnetic image is thus formed in the magnetizable layer corresponding to the imagewise arrangement of magnetized toner particles.
Concurrently with the growth of interest in magnetic imaging there has been increased interest in magnetic developers to render the latent magnetic images visible. In U.S. Pat. No. 3,221,315 there is described the use of encapsulated ferrofluids in a magnetic recording medium, wherein the ferrofluid orientation in the presence of a magentic field exhibits a variable light responsive characteristic. In this situation the magnetic recording medium is self-developing in the sense that magnetic marking material need not be employed to render a visible image. In other situations latent magnetic images are rendered visible by magnetic marking material. Thus, for example, in U.S. Pat. No. 3,627,682, there is disclosed binary toners for developing latent magnetic iamges, which binary toners include a particulate hard magnetic material and a particulate soft magnetic material in each toner particle. The toner particles include two materials in a binder material. In U.S. Pat. No. 2,826,634 there is described the use of iron or iron oxide particles either alone or encapsulated in low melting resin or binders for developing latent magnetic images.
Other patents evidencing the continuing interest in improved magnetic developers include U.S. Pat. No. 3,520,811, which discloses that magnetic particles of chromium dioxide appear to catalyze a surface polymerization or organic air drying film forming vehicles such as those employed in oil base materials in order that a coating of polymerized vehicle is formed around the particle; and U.S. Pat. No. 3,905,841 which teaches the prevention of agglomeration and the formation of homogeneous dispersions of cobalt-phosphorous particles into an organic resin binder by treatment with a solution containing sulfuric acid.
Typical fusing methods used in magnetic imaging that have been described in the prior art include, for example, heating the toner image to cause the resins thereof to at least partially melt and become adhered to the transfer medium followed by application of pressure to the toner, such as use of a heated roller. Solvent or solvent vapor fusing has also been used, wherein the resin component of the toner is partially dissolved.
In order to render magnetic imaging systems more amenable to higher speed duplicating machines, a non-contact flash fusing system, such as that well known in electrophotographic machines, should be used. Aside from higher process speed, improved reliability, especially for paper handling, and higher copy quality is attained. However, in general, toner materials which function satisfactorily with a hot-pressure roll fuser do not perform satisfactorily with a flash fuser. This is true because of the significantly different process-related rheological criteria between these two systems. For contact pressure roll fusing, one needs a toner with shear-dependent viscosity (i.e., low viscosity at high shear and relatively high viscosity at low shear) and sufficient viscoelasticity to avoid hot set-off to the fuser roll over the fusing temperature interval of interest. On the other hand, for non-contact flash fusing, one desires a toner with a strongly temperature-dependent viscosity and minimal elasticity such that the molten toner will rapidly flow and penetrate the paper fibers at the fusing temperature without benefit of contact induced shear. Specifically, for magnetic imaging systems, where the high pigment loading required for development can have an adverse effect on the desired fusing level of the toner, the toner materials designed for and found most acceptable in roll fusing do not have the desired rheological properties for flash fusing.